The present invention is related to reciprocating piston air compressors of the type having a cylinder wall with slots for controlling the inlet of pre-compressed air to be compressed and with at least one outlet valve in the cylinder head for the removal of the compressed air.
An air compressor of this general type is known from German Patent Specification 304,021. In this air compressor, the pre-compression occurs in a chamber at the rear side of the piston, only a small degree of compression being obtained. The valve located in the cylinder head and connecting the cylinder space with the external air (air inlet) is a spring-loaded snuffler valve which does not open during the piston return stroke until the pressure in the cylinder space becomes less than the external pressure.
The invention is based on the objective of increasing the delivery of the air compressor and the final pressure of the compressed air, particularly in conjunction with an improved volumetric efficiency.
The present invention solves these problems by providing a second valve connecting the cylinder space with the external air and by controlling the second valve as a function of the compressor crankshaft angle in such a way that it opens during the piston return stroke between the closing of the outlet valve and the opening of the slots and connects the cylinder space with an additional dead or storage space which is in turn connected with the external air.
Using a turbo-charger, a substantially higher pre-compression pressure is obtainable than in the case of the known air compressor. The possibly higher thermal loading resulting from this arrangement, the main effect of which is to have an unfavorable influence on the efficiency of the air compressor, is reduced in the subject of the invention by the fact that the compressed hot air remaining in the cylinder space after the closing of the outlet valve at the beginning of the piston return stroke flows into the additional dead space via the open regulating valve and that during the subsequent return strokes, cooler air is induced via the regulating valve until, after the opening of the slots, the pre-compressed air flows into the cylinder space. The replacement of the hot air by the cooler air and the cooling of the cylinder sleeve associated therewith increases the cylinder volumetric efficiency and hence the efficiency and delivery of the air compressor.
In an especially preferred embodiment, during idling operation of the compressor, the regulating valve is continuously open and respective shut-off valves close the passage between the turbo-compressor and the air compressor and the passage from the additional dead space to the external air.
In this arrangement the cylinder dead space and the additional dead space connected with it via the open regulating valve are so large that practically no compression of the air enclosed thereby occurs, and hence the power consumption of the air compressor during idling is advantageously very small.
Using an air compressor comprising several similarly constructed compressor cylinders, high pressures are obtainable by stepwise air compression without the intermediate connection of an expensive air cooler being necessary. The limitation of the temperature of the compressed air obtainable using the invention is so substantial that the compression of the air to a high level occurs with a good volumetric efficiency and the final temperature of the air remains below certain values prescribed for use in a motor vehicle. Intermediate air receivers can be used with multiple cylinder compressor embodiments as needed.
Further objects, features, and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawing which shows, for purposes of illustration only, one embodiment in accordance with the present invention .